Glycolic acid has conventionally been used mainly as boiler compounds, cleaning agents, leather tanning agents, chelating agents of a metal ion and the like. In recent years, it expands its application to cosmetics and drugs for external use. Glycolic acid to be used as a drug for external use is desired to contain a lower level of harmful impurities. Glycolic acid has recently been expected also as a raw material for polyglycolic acid having biodegradability and a gas barrier function.
Typical examples of a conventionally known method for producing glycolic acid include (1) a method of reacting carbon monoxide, formaldehyde and water in the presence of a strongly acidic catalyst under high-temperature and high-pressure conditions, (2) a method of reacting chloroacetic acid with sodium hydroxide, (3) a method of carrying out a Cannizzaro reaction between glyoxal available by oxidation of ethylene glycol and a strong alkali to form a glycolate salt, and then adding an acid to liberate glycolic acid from the resulting glycolate salt; (4) a method of carrying out a liquid-phase reaction between glyoxal available by oxidation of ethylene glycol and water in the presence of an inorganic catalyst; (5) a method for catalytic oxidation of ethylene glycol in the presence of a noble metal catalyst and oxygen; and (6) a method of carrying out oxidative esterification of ethylene glycol with methanol and oxygen to obtain methyl glycolate and then hydrolyzing into glycolic acid.
The method of reacting carbon monoxide, formaldehyde and water in the presence of a strongly acidic catalyst under high-temperature and high-pressure conditions includes, for example, a method of reacting formaldehyde and carbon monoxide in an aqueous organic solvent in the presence of a hydrogen fluoride catalyst (refer to, for example, Patent Document 1) and a method of reacting formaldehyde and carbon monoxide in an aqueous medium in the presence of a sulfuric acid catalyst (refer to, for example, Patent Documents 2 and 3).
This method has a problem that glycolic acid must be produced by using special reaction equipment and special reaction conditions of high temperature and high pressure. In addition, it inevitably produces byproducts such as organic acids, for example, formic acid or methoxyacetic acid showing mutagenicity. Glycolic acid obtained using reaction conditions of high temperature and high pressure contains a large amount of various impurities such as methanol due to side reaction and sulfuric acid used as the catalyst. This method needs a large amount of labor and energy for removal of these impurities to purify the reaction product and is therefore inefficient. In addition, this method requires both an anion exchange resin and a cation exchange resin. Described specifically, the steps constituting this method are very complicated, because anion exchange resin, live steam stripping and cation exchange resin are necessary for the removal of sulfuric acid, low-boiling-point impurities, and metal impurities, respectively.
The method (2) of reacting monochloroacetic acid with sodium hydroxide (refer to, for example, Patent Documents 4 and 5) requires use of an about stoichiometric amount of sodium hydroxide. This leads to a problem that sodium chloride contaminated with an organic matter appears stoichiometrically as a waste material. Moreover, owing to sodium chloride generated stoichiometrically as a by-product raises the slurry concentration after concentration, leading to poor operability and a large loss. Another problem is that a salt is not removed completely and remains in the product.
A problem common to the methods (3) to (6) is that since ethylene glycol is produced using ethylene oxide as a raw material, a step of producing ethylene glycol is long and in addition, ethylene oxide which is explosive must be handled in the production process.
The production method of (3) is a method of carrying out a Cannizzaro reaction between glyoxal available by oxidation of ethylene glycol and a strong alkali to form a glycolate salt, and then adding an acid to liberate glycolic acid from the resulting glycolate salt (refer to, for example, Non-patent documents 1 and 2). The Cannizzaro reaction is a disproportionation reaction so that a large amount of byproducts is generated, which results in a deterioration in the productivity and formation of a large amount of impurities.
The production method (4) is a method of carrying out a liquid-phase reaction between glyoxal available by oxidation of ethylene glycol and water in the presence of an inorganic catalyst (refer to, for example, Patent Document 6). In this method, a component of the metal salt used as the catalyst is mixed in the solution obtained by the reaction so that a step of removal of it is necessary. A purification step for the removal of the metal salt component from the solution obtained by the reaction is industrially complex and difficult so that necessity of it is a great drawback of this method.
The production method (5) is a method for catalytic oxidation of ethylene glycol in the presence of a noble metal catalyst and oxygen (refer to, for example, Patent Document 7). This method has drawbacks such as inevitable use of a noble metal such as platinum which is expensive and is a scarce resource; poor productivity due to long reaction time; and generation of many kinds of byproducts because the selectivity to glycolic acid is low owing to the oxidation reaction.
The production method (6) is a method of carrying out oxidative esterification of ethylene glycol with methanol and oxygen to obtain methyl glycolate and then hydrolyzing into glycolic acid (refer to, for example, Patent Document 8). This method has drawbacks such as inevitable use of a noble metal such as gold which is expensive and is a scarce resource and generation of many kinds of byproducts because of a low selectivity to methyl glycolate in the oxidative esterification.
The conventional production methods have the above-described problems. In particular, glycolic acid obtained by these methods is insufficient as a monomer for polymerization into polyglycolic acid.
As a production method of glycolonitrile, a method of preparing glycolonitrile from formaldehyde and hydrocyanic acid (refer to, for example, Patent Documents 9 to 13) and an oxidation method of acetonitrile (refer to, for example, Patent Documents 14 and 15) are known. According to these known documents, glycolonitrile obtained from formaldehyde and hydrocyanic acid is used as a raw material for glycine or hydantoin.
A method of preparing ammonium glycolate by hydrolyzing glycolonitrile by using microorganisms in the presence of an aqueous solvent is also known (refer to, for example, Patent Documents 16 to 18). These documents however do not include a description on the production method of glycolonitrile.
This means that a method using hydrocyanic acid as a starting raw material is not known as a production method of glycolic acid.
Patent Document 1: Japanese Patent Laid-Open No. 59-139341
Patent Document 2: U.S. Pat. No. 2,153,064
Patent Document 3: International Patent Publication No. 6-501268
Patent Document 4: Japanese Patent Laid-Open No. 62-77349
Patent Document 5: Japanese Patent Laid-Open No. 9-67300
Non-patent Document 1: Chem. Ber. 54, 1395 (1921)
Non-patent Document 2: Acta Chem. Scand. 10, 311 (1956)
Patent Document 6: Japanese Patent Publication No. 6-35420
Patent Document 7: Japanese Patent Publication No. 60-10016
Patent Document 8: Japanese Patent Laid-Open No. 2004-43386
Patent Document 9: Japanese Patent Laid-Open No. 62-267257
Patent Document 10: Japanese Patent Laid-Open No. 53-68725
Patent Document 11: Japanese Patent Laid-Open No. 6-135923
Patent Document 12: Japanese Patent Publication No. 53-18015
Patent Document 13: Japanese Patent Laid-Open No. 51-100027
Patent Document 14: U.S. Pat. No. 4,634,789
Patent Document 15: U.S. Pat. No. 4,515,732
Patent Document 16: Published Japanese Translation of PCT International Publication No. 2005-504506
Patent Document 17: Japanese Patent Laid-Open No. 9-28390
Patent Document 18: Japanese Patent Laid-Open No. 61-56086